Most aches and pains are in part underlying imbalances. Look at this through whatever lens you like: chiropractic alignment; MAT activation; RPR sequencing; OPT cross syndromes; FMS analysis; the list goes on. The point is that modern life has an adducted and flexed knee, a plantar flexed and pronated foot, and everted ankle. Sitting, sitting, sitting. And then, even when people are standing, forget about the foot, ankle, knee and hip aligning. They’re a mess, and fibrotically fixed in those high torsion positions as well. Thus, at some point, you should probably do the OPPOSITE. Well, here is the opposite: fixed knee extension with variant quad lengths/forces. Video here: https://www.instagram.com/p/B58WVe3D49r/
Especially for people with tissue deformities or overt knee injuries, it’s critical that you begin in a corrective/endurance loading and rep range (no or very light ankle weight at 15-25 reps). Maintaining knee extension and slightly inverted ankle dorsiflexion, flex at the hip. If you watch closely I’m showcasing how you can rotate at the hip in order to change quad emphasis (along with reduce possible psoas irritation). With a cable or ankle weights, even advanced athletes can use this as sufficient stimulus, although a layperson without joint irregularities and high level athletes will ultimately require vertical loading, compressive forces, compound exercise, and even impact.
Rotation inward calls upon more vastus lateralis. External rotation call upon more medialis. This particular exercise also capitalizes on constant reciprocal inhibition, such that it makes for good mobilizing and retraining of the knee flexors, gastroc and soleus concurrently.